Optical sensor

ABSTRACT

Photodetector  1  is equipped with photodiodes PDn, integrating circuits  10   n , CDS circuits  20   n , and hold circuits  30   n . Each integrating circuit  10   n  includes an amplifier  11   n , a capacitor C, and a switch SW. Photodiodes PDn are aligned on a first substrate  100 . A differential pair input part (transistors T 1  and T 2 ) of amplifier  11   n , capacitor C, etc., of each integrating circuit  10   n  are disposed on a second substrate  200 . A drive part (transistors T 5  and T 6 ) of amplifier  11   n , etc., of each integrating circuit  10   n  are disposed on a third substrate  300.

FIELD OF THE ART

This invention concerns a photodetector wherein a plurality ofphotodiodes are aligned.

BACKGROUND ART

A photodetector is equipped with a plurality of photodiodes, which arealigned one-dimensionally or two-dimensionally, and integratingcircuits, which include amplifiers and capacitors, and may be equippedin some cases with a signal processing circuit at a more downstreamposition. With this photodetector, charges of amounts, which are inaccordance with the intensities of incident light on the respectivephotodiodes, are output from the photodiodes, these charges areaccumulated in the capacitors, and voltages, which are in accordancewith the amounts of these accumulated charges, are output from theintegrating circuits. Based on the voltages output from the integratingcircuits in accordance with the amounts of charges generatedrespectively at the plurality of photodiodes, the light, made incidenton a light receiving part wherein the plurality of photodiodes arealigned, is detected.

As such a photodetector, the arrangement disclosed in Japanese PublishedUnexamined Patent Application No. Hei 11-287863 is known. With thephotodetector disclosed in this publication, a first substrate, whereina plurality of photodiodes are aligned two-dimensionally, and a secondsubstrate, wherein integrating circuits, etc., are disposed, areconnected to each other by a flexible cable. Also, a switch array isdisposed on the first substrate on which the plurality of photodiodearrays are aligned, and by the on/off of the respective switches in thisswitch array, one or more of the photodiodes of the two-dimensionallyaligned plurality of photodiodes are selected and connected to theintegrating circuits.

DISCLOSURE OF THE INVENTION

However, with the photodetector disclosed in the above-mentionedpublication, wiring, which connect the respective photodiodes and therespective switches to each other, exist in a region between theplurality of photodiodes aligned on the first substrate, and the numberof such wiring is extremely large. If the first substrate is to beincreased in the number of photodiodes (number of pixels) or made highin density, even more wiring will be required in a narrow region.Increasing of the number of pixels and the realization of high densityare thus difficult. Also, since the wiring become long, noise becomessuperposed readily on the charges that are sent from the photodiodes tothe integrating circuits, thus disabling accurate photodetection.

In order to resolve such a problem, bump-connecting the first substrate,in which the plurality of photodiodes are aligned two-dimensionally, andthe second substrate, in which the integrating circuits, etc., aredisposed, to each other may be considered. By bump connection, thenumber of wiring on the first substrate can be reduced or the wiring canbe made short, thus enabling the first substrate to be increased in thenumber of pixels and made high in density.

However, in the case of bump connection, the photodiodes on the firstsubstrate and the amplifiers, included in the integrating circuits onthe second substrate, will be positioned close to each other. Thetemperature of the photodiodes on the first substrate will thus rise dueto heat generation by the amplifiers on the second substrate, and due tothis temperature rise, accurate photodetection will be disabled.

This invention has been made to resolve the above problems, and anobject thereof is to provide a photodetector, enabling increase of thenumber of pixels and realization of high density and yet enablingaccurate photodetection.

This invention's photodetector comprises: (1) a plurality ofphotodiodes, each generating charges of an amount that is in accordancewith the intensity of incident light; and (2) integrating circuits, eachincluding an amplifier, having a differential pair input part at theinput end side and a drive part at the output end side, and a capacitorand a switch, which are disposed between the input end and the outputend of the amplifier, and, when the switch is opened, accumulating, inthe capacitor, charges input into the input end from a photodiode andoutputting, from the output end, a voltage that is in accordance withthe amount of charges accumulated in the capacitor.

This invention's photodetector is also characterized in that theplurality of photodiodes are disposed on a first substrate, thecapacitors and the differential pair input parts are disposed on asecond substrate, the drive parts are disposed on a third substrate, andthe photodiodes and the input ends of the integrating circuits areelectrically connected to each other by the first substrate and secondsubstrate being bump-connected to each other. It is furthermorepreferable for the second substrate and third substrate to bebump-connected to each other.

Or this invention's photodetector is characterized in that the pluralityof photodiodes are disposed on a first substrate, the capacitors, thedifferential pair input parts, and the drive parts are disposed on asecond substrate, the photodiodes and the input ends of the integratingcircuits are electrically connected to each other by the first substrateand second substrate being bump-connected to each other, the capacitorsand differential pair input parts are disposed in a first region on thesecond substrate that overlaps with a region on the first substrate inwhich the plurality of photodiodes are disposed, and the drive parts aredisposed in a second region on the second substrate that does notoverlap with the region on the first substrate in which the plurality ofphotodiodes are disposed.

With this invention, when light is made incident on the first substrate,charges of amounts, which are in accordance with the incidentintensities, are generated from the respective photodiodes of the firstsubstrate. These charges are input into the integrating circuits on thesecond substrate (or in the first region of the second substrate), whichis bump-connected to the first substrate, and accumulated in thecapacitors. Voltages, which are in accordance with the amounts ofcharges accumulated in the capacitors, are then output from the driveparts of the integrating circuits on the third substrate (or in thesecond region of the second substrate).

With this invention, the differential pair input parts of the amplifiersand the capacitors of the integrating circuits are disposed on thesecond substrate (or in the first region of the second substrate), whichis bump-connected to the first substrate. Meanwhile, the drive parts ofthe amplifiers of the integrating circuits are disposed on a thirdsubstrate (or in the second region of the second substrate), which isnot bump-connected to the first substrate. The photodetector of thisinvention thus enables the number of pixels to be increased and a highdensity to be realized and yet enables accurate photodetection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a photodetector 1 of an embodiment.

FIG. 2 is a detailed circuit diagram of integration or integratingcircuit 10 n of photodetector 1 of the embodiment.

FIG. 3 is a perspective view showing the positional relationship of afirst substrate 100, a second substrate 200, and a third substrate 300of photodetector 1 of the embodiment.

FIG. 4 is a diagram showing an example of a cross section of firstsubstrate 100 and second substrate 200 of photodetector 1 of theembodiment.

FIG. 5 is a diagram showing another example of a cross section of firstsubstrate 100 and second substrate 200 of photodetector 1 of theembodiment.

FIG. 6 is a perspective view showing the positional relationship of afirst substrate 100 and a second substrate 210 of a photodetector 2 ofanother embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of this invention shall now be described in detail withreference to the drawings. In the description of the drawings, the sameelements shall be provided with the same symbols and redundantdescription shall be omitted.

FIG. 1 is a schematic view of a photodetector 1 of an embodiment. Thisphotodetector 1 is equipped with N photodiodes PD₁ to PD_(N), Nintegrating circuits 10 ₁ to 10 _(N), N CDS (Correlated Double Sampling)circuits 20, to 20 _(N), and N hold circuits 30, to 30 _(N). Here, N isan integer of no less than 2. Each photodiode PD_(n), generates chargesof an amount that is in accordance with the intensity of incident light.Here, n is an integer no less than 1 and no more than N. Eachintegrating circuit 10 _(n) inputs the charges generated by photodiodePD_(n), accumulates these charges in a capacitor, and outputs a voltagethat is in accordance with the amount of accumulated charges. Each CDScircuit 20 _(n) inputs the voltage output from integrating circuit 10_(n) and outputs a voltage expressing the variation amount of the inputvoltage within a fixed time. Each hold circuit 30, inputs the voltageoutput from CDS circuit 20 _(n), holds this voltage for a fixed periodand outputs this voltage.

FIG. 2 is a detailed circuit diagram of an integrating circuit 10 _(n)of photodetector 1 of the present embodiment. With each photodiodePD_(n), an anode terminal is grounded and a cathode terminal isconnected to an input end of an amplifier 11 _(n) of integrating circuit10 _(n). Integrating circuit 10 _(n) includes amplifier 11 _(n), acapacitor C, and a switch SW. Capacitor C and switch SW are mutuallyconnected in parallel and are disposed between the input end and outputend of amplifier 11 _(n). A CDS circuit 20, is connected to the outputend of amplifier 11 _(n). With this integrating circuit 10 _(n), withthe closing of switch SW, capacitor C is discharged and the outputvoltage is initialized. Meanwhile, during the period in which switch SWis open, the charges input into the input end from photodiode PD_(n) areaccumulated in capacitor C and a voltage, which is in accordance withthe amount of charges accumulated in this capacitor C, is output fromthe output end.

Amplifier 11 _(n) has FET type transistors T₁ to T₇. Of these,transistors T₁, T₂, T₆, and T₇ are NMOS transistors, and transistors T₃,T₄, and T₅ are PMOS transistors. The gate terminal of transistor T₁ isconnected to the input end of amplifier 11 _(n). The source terminal oftransistor T₁ and the source terminal of transistor T₂ are respectivelyconnected to the drain terminal of transistor T₇. The source terminal oftransistor T₇ is grounded. The drain terminal of transistor T₁ isconnected to the gate terminal and the drain terminal of transistor T₃and the gate terminal of transistor T₄. The drain terminal of transistorT₂ is connected to the drain terminal of transistor T₄ and the gateterminal of transistor T₅. The drain terminal of transistor T₅ isconnected to the drain terminal of transistor T₆ and to the output endof amplifier 11 _(n). The source terminal of transistor T₆ is grounded.A predetermined voltage is input into the source terminal of each oftransistors T₃ to T₅. A predetermined DC voltage is input into the gateterminal of each of transistors T₂, T₆, and T₇. In order to preventoscillation as an amplifier, a capacitor and a resistor element areconnected in series between the drain and the gate of transistor T₅ asshown in FIG. 2.

Of these transistors T₁ to T₇, transistors T_(1 and T) ₂ at the inputend side form a differential pair input part of amplifier 11 _(n). Also,transistors T₅ and T₆ at the output end side form a drive part ofamplifier 11 _(n). Whereas the amount of heat generated by thedifferential pair input part is comparatively low, the amount of heatgenerated by the drive part is comparatively high.

Also as shown in FIGS. 1 and 2, photodetector 1 of the presentembodiment is divided among the three substrates of a first substrate100, a second substrate 200, and a third substrate 300. That is, the Nphotodiodes PD₁ to PD_(N) are aligned one-dimensionally ortwo-dimensionally on first substrate 100. On second substrate 200 arepositioned the differential pair input part of amplifier 11 _(n),capacitor C, and switch SW of each of the N integrating circuits 10 ₁ to10 _(N). On third substrate 300 are positioned the drive part and theother transistors T₃, T₄, and T₇ of amplifier 11 _(n) of each of the Nintegrating circuits 10 ₁ to 10 _(N), as well as the N CDS circuits 20 ₁to 20 _(N) and the N hold circuits 30 ₁ to 30 _(N).

FIG. 3 is a perspective view showing the positional relationship offirst substrate 100, second substrate 200, and third substrate 300 ofphotodetector 1 of the present embodiment. In actuality, substrates 100and 200 are electrically connected to each other and substrates 200 and300 are electrically connected to each other through bump electrodes. Asshown in FIG. 3, with photodetector 1 of the present embodiment, therespective substrates are mounted so as to overlap in the direction ofincidence of light, and first substrate 100 and second substrate 200 arebump-connected to each other and second substrate 200 and thirdsubstrate 300 are bump-connected to each other.

When light is made incident on first substrate 100, charges of anamount, which is in accordance with the incident light amount, areoutput from each photodiode PD_(n), and these charges are input fromfirst substrate 100 via the bump connection into the input end of thecorresponding integrating circuit 10 _(n) on second substrate 200. Avoltage, which is in accordance with the amount of charges generated atphotodiode PD_(n), is then output from integrating circuit 10 _(n) thatincludes amplifier 11 _(n), which is disposed across both secondsubstrate 200 and substrate 300, and capacitor C and switch SW, whichare disposed on second substrate 200. A voltage expressing the variationamount over a fixed time of the voltage output from integrating circuit10 _(n) is then output from CDS circuit 20 _(n), disposed on thirdsubstrate 300, and the voltage output from CDS circuit 20 _(n) is thenheld for a fixed period and then output by hold circuit 30 _(n),disposed on third substrate 300 FIG. 4 is a diagram showing an exampleof a cross section of first substrate 100 and second substrate 200 ofphotodetector 1 of the present embodiment. Since in FIG. 4, a basicpattern is repeated in the left and right directions, the followingdescription shall concern only a single basic pattern.

With first substrate 100, on a first surface (the upper side surface inFIG. 4) of an n-type semiconductor substrate are formed a p⁺ region 111,which forms a pn junction with the n-type substrate and thereby makes upa photodiode PD, and an n⁺ region 112, which serves as an isolationregion. Also, with first substrate 100, on a second surface (the lowerside surface in FIG. 4) of the n-type semiconductor substrate are formedan n⁺-type impurity layer 121, which forms an ohmic connection with ametal electrode 124, an insulating protective layer 122, for protectingthe surface, and metal electrode 124, which passes through protectivelayer 122 and is electrically connected with n⁺-type impurity layer 121.Furthermore, first substrate 100 has a through hole 131, passing throughbetween the first surface and the second surface, and a throughelectrode 131 is disposed in this through hole. A metal wiring layer113, which electrically connects p⁺ region 111 and through electrode131, is formed on the first surface side of first substrate 100, and ametal electrode 123, which is electrically connected with throughelectrode 131, is formed on the second surface side.

With second substrate 200, a metal electrode 223, which is electricallyconnected to the input end of an integrating circuit 10 _(n), and ametal electrode 224, which is electrically connected to a groundpotential, are formed on a first surface (the upper side surface in FIG.4) of a semiconductor substrate. Metal electrode 123 of first substrate100 and metal electrode 223 of second substrate 200 are connected toeach other by a bump 423, and metal electrode 124 of first substrate 100and metal electrode 224 of second substrate 200 are connected to eachother by a bump 424. The gap between first substrate 100 and secondsubstrate is filled with a resin.

Also, on the first surface side of first substrate 100 are positioned ascintillator 510 and a shielding member 520. Scintillator 510 isdisposed above p⁺ region 111 of first substrate 100 and generatesscintillation light upon incidence of X-rays or other energy rays.Shielding material 520 is disposed above n⁺ region 112 of firstsubstrate 100, blocks the transmission of X-rays and other energy rays,and fixes scintillator 510.

With the arrangement shown in FIG. 4, when X-rays or other energy raysare made incident into scintillator 510, scintillation light isgenerated by scintillator 510. When this scintillation light is thenmade incident on p⁺ region 111 of first substrate 100, charges aregenerated at the pn junction part. These charges are input, via metalwiring layer 113, through electrode 131, metal electrode 123, bump 423,and then metal electrode 223 of second substrate 200, into the input endof integrating circuit 10 _(n), which is formed on second substrate 200.If switch SW of integrating circuit 10 _(n) is open, the charges inputinto the input end are accumulated in capacitor C. A voltage, which isin accordance with the amount of charges accumulated in capacitor C, isthen output from the drive part of integrating circuit 10 _(n), which isformed on third substrate 300.

FIG. 5 is a diagram showing another example of a cross section of firstsubstrate 100 and second substrate 200 of photodetector 1 of the presentembodiment. Since a basic pattern is repeated in the left and rightdirections in FIG. 5 as well, the following description shall concernonly a single basic pattern.

With first substrate 100, on a first surface (the upper side surface inthe FIG. 5) of an n-type semiconductor substrate are formed an n⁺-typeaccumulation layer 151 for preventing charge recombination and aninsulating protective layer 152 for protecting the surface. With firstsubstrate 100, on a second surface (the lower side surface in the FIG.5) of the n-type semiconductor substrate are formed a p⁺ region 161,which forms a pn junction with the n-type substrate and thereby makes upa photodiode PD, and an n⁺ region 162, which serves as an isolationregion, and a protective layer 163 is formed above these regions. Alsoon the second surface of first substrate 100 are formed a metalelectrode 164, which is electrically connected with p⁺ region 161, and ametal electrode 165, which is electrically connected with n⁺ region 162.

With second substrate 200, metal electrodes 264 and 265, which areelectrically connected to the input end of an integrating circuit 10_(n), are formed on a first surface (the upper side surface in the FIG.5) of a semiconductor substrate. Metal electrode 164 of first substrate100 and metal electrode 264 of second substrate 200 are connected toeach other by a bump 464, and metal electrode 165 of first substrate 100and metal electrode 265 of second substrate 200 are connected to eachother by a bump 465. The gap between first substrate 100 and secondsubstrate is filled with a resin.

Also, on the first surface of first substrate 100 are positioned ascintillator 510 and a shielding member 520. Scintillator 510 isdisposed above p⁺ region 161 of first substrate 100 and generatesscintillation light upon incidence of X-rays or other energy rays.Shielding material 520 is disposed above n+region 162 of first substrate100, blocks the transmission of X-rays and other energy rays, and fixesscintillator 510. Also with first substrate 100, at the part at which p⁺region 161 is formed, the first surface side is made thin in thicknessby chemical-mechanical polishing, anisotropic etching, etc.

With the arrangement shown in FIG. 5, when X-rays or other energy raysare made incident into scintillator 510, scintillation light isgenerated by scintillator 510. When this scintillation light is thentransmitted through first substrate 100 and made incident on p⁺ region161, charges are generated at the pn junction part. These charges areinput, via metal wiring layer 164, bump 464, and then metal electrode264 of second substrate 200, into the input end of integrating circuit10 _(n), which is formed on second substrate 200. If switch SW ofintegrating circuit 10 _(n) is open, the charges input into the inputend are accumulated in capacitor C. A voltage, which is in accordancewith the amount of charges accumulated in capacitor C, is then outputfrom the drive part of integrating circuit 10 _(n), which is formed onthird substrate 300.

Thus with this embodiment's photodetector 1 of either of thearrangements shown in FIGS. 4 and 5, charges that are generated in eachphotodiode PD_(n) on first substrate 100 are input into the input end ofintegrating circuit 10 _(n) on second substrate 200, which isbump-connected to this first substrate 100, and accumulated in capacitorC. A voltage that is in accordance with the amount of charges incapacitor C is then output from the drive part of integrating circuit 10_(n) on third substrate 300.

The wiring on first substrate 100 can thus be lessened in amount orshortened to enable an increased number of pixels and high density to berealized readily on the first substrate. Also, since the charge transferpath from photodiode PD_(n) on first substrate 100 to the differentialpair input part of amplifier 11 _(n) and capacitor C of integratingcircuit 10 _(n) on second substrate 200 can be shortened, thesuperposition of noise is restrained, and accurate photodetection isthereby enabled. Also, though the drive part of amplifier 11 _(n) ofeach integrating circuit 10 _(n) on third substrate 300 is high in heatgeneration amount, since it is disposed away from first substrate 100,on which each photodiode PD_(n) is formed, temperature rise of eachphotodiode PD_(n) on first substrate 100 is restrained and accuratephotodetection is enabled from this point as well. This embodiment isalso favorable in that optimal manufacturing processes can be employedfor first substrate 100, on which a photodiode array is formed, and forsecond substrate 200 and third substrate 300, on which signal processingcircuits, such as the integrating circuits, are formed.

FIG. 6 is a perspective view showing the positional relationship of afirst substrate 100 and a second substrate 210 of a photodetector 2 ofanother embodiment. First substrate 100 of this photodetector 2 is thesame in arrangement as first substrate 100 of the above-describedphotodetector 1 and has N photodiodes PD₁ to PD_(n) formed thereon.Meanwhile, second substrate 210 is substantially the same as anarrangement in which second substrate 200 and third substrate 300 of theabove-described photodetector 1 are put together.

Second substrate 210 of this photodetector 2 includes a first region 211and a second region 212. First region 211 of second substrate 210 isconnected by a bump B to first substrate 100, thereby electricallyconnecting a photodiode PD_(n) and the input end of an integratingcircuit 10 _(n) to each other. First region 211 of second substrate 210is a region that overlaps with a region on first substrate 100 on whichphotodiodes PD₁ to PD_(N) are disposed and, as with second substrate 200of the above-described photodetector 1, has capacitor C and thedifferential pair input part of amplifier 11 _(n) of integrating circuit10 _(n) disposed therein. Meanwhile, second region 212 of secondsubstrate 210 is a region that does not overlap with the region on firstsubstrate 100 on which photodiodes PD₁ to PD_(N) are disposed and, aswith third substrate 300 of the above-described photodetector 1, has thedrive part of amplifier 11 _(n) of integrating circuit 10 _(n) disposedtherein.

With this photodetector 2, charges that are generated in each photodiodePD_(n) on first substrate 100 are input into the input end ofintegrating circuit 10 _(n) in first region 211 of second substrate 210,which is bump-connected to this first substrate 100, and accumulated incapacitor C. A voltage that is in accordance with the amount of chargesin capacitor C is then output from the drive part of integrating circuit10 _(n) in second region 212 of second substrate 210, which does notoverlap with first substrate 100. The same effects as those exhibited bythe above-described photodetector 1 can thus be exhibited.

This invention is not limited to the embodiments described above, andvarious modifications are possible. For example, the amplifier includedin the integrating circuit is not limited to that of the arrangementshown in FIG. 2 and may be of another arrangement. Also, the respectivecross-sectional structures of first substrate 100 and second substrate200 are not restricted to those shown in each of FIGS. 4 and 5. Alsoanother circuit (for example, an A/D conversion circuit, etc.,) may bedisposed on third substrate 300 or in second region 212 of secondsubstrate 210.

As described in detail above, with the present invention, thedifferential pair input parts of amplifiers and capacitors ofintegrating circuits are disposed on a second substrate (or in a firstregion of a second substrate), which is connected by bumps to a is firstsubstrate. Meanwhile, the drive parts of the amplifier of theintegrating circuits are disposed on a third substrate (or in a secondregion of the second substrate), which is not bump-connected to thefirst substrate. Thus with this invention's photodetector, increasednumber of pixels and high density can be realized while enablingaccurate photodetection.

INDUSTRIAL APPLICABILITY

This invention can be used in a photodetector.

1. A photodetector comprising: a plurality of photodiodes, eachgenerating charges of an amount that is in accordance with the intensityof incident light; and integrating circuits, each including anamplifier, having a differential pair input part at the input end sideand a drive part at the output end side, and a capacitor and a switch,which are disposed between said input end and said output end of saidamplifier, and, when said switch is opened, accumulating, in thecapacitor, charges input into said input end from an above-mentionedphotodiode and outputting, from said output end, a voltage that is inaccordance with the amount of charges accumulated in said capacitor,said plurality of photodiodes being disposed on a first substrate, saidcapacitors and said differential pair input parts being disposed on asecond substrate, said drive parts being disposed on a third substrate,and said photodiodes and said input ends of said integrating circuitsbeing electrically connected to each other by said first substrate andsaid second substrate being bump-connected to each other.
 2. Thephotodetector according to claim 1, wherein said second substrate andsaid third substrate are bump-connected to each other.
 3. Aphotodetector comprising: a plurality of photodiodes, each generatingcharges of an amount that is in accordance with the intensity ofincident light; and integrating circuits, each including an amplifier,having a differential pair input part at the input end side and a drivepart at the output end side, and a capacitor and a switch, which aredisposed between said input end and said output end of said amplifier,and, when said switch is opened, accumulating, in the capacitor, chargesinput into said input end from an above-mentioned photodiode andoutputting, from said output end, a voltage that is in accordance withthe amount of charges accumulated in said capacitor, said plurality ofphotodiodes being disposed on a first substrate, said capacitors, saiddifferential pair input parts, and said drive parts being disposed on asecond substrate, said photodiodes and said input ends of theintegrating circuits being electrically connected to each other by saidfirst substrate and said second substrate being bump-connected to eachother, said capacitors and said differential pair input parts beingdisposed in a first region on said second substrate that overlaps with aregion on said first substrate in which said plurality of photodiodesare disposed, and said drive parts are disposed in a second region onsaid second substrate that does not overlap with the region on saidfirst substrate in which said plurality of photodiodes are disposed.